The mechanisms of resistance to HIV-1 infection in the human oral cavity are incompletely understood. While salivary components have been implicated in protection, there is growing evidence that human defensins may be playing an important role in prevention of HIV infection. New antiviral, chemotaxis and immunosurveillance properties are being attributed to beta-defensins; small cationic antimicrobial innate response molecules expressed in mucosal epithelium. Inducible beta-defensins are always expressed in normal oral epithelium, a property not shared by other mucosal barriers. Certain oral commensal bacteria may contribute to this induction. We have shown that normal human oral epithelial cells (NHOECS) express the known beta-defensins and that Fusobacterium nucleatum, a ubiquitous bacterium of the oral cavity, upregulates human beta-defensin 2 (hBD2), resulting in protection from invasive bacteria. We now demonstrate that HIV-1 X4 and R5 viral phenotypes induce hBD2 mRNA in NHOECs and that hBD2 and -3 inhibit HIV-1 infection by both viral strains, with greater activity against X4 viruses. This proposal intends to test hypotheses emanating from the postulate that oral epithelial cells can be stimulated to produce beta-defensins that protect the host from HIV-1 at the oral mucosal barrier. The objectives of this proposal are (1) to study mechanisms of induction of hBD2 by HIV-1 in NHOECs, (2) to analyze the mechanisms by which hBD2 and -3 inhibit HIV-1 infectivity, and (3) to test the F. nucleatum hBD2 induction model for protection against HIV-1. Relative resistance to infection by the X4 phenotype, at mucosal sites, may in part be attributed to beta-defensins. Recent developments in defensin biology, coupled with our new observations, will facilitate rapid exploration of this newly discovered antiviral defense mechanism and may lead to future studies of HIV microbicidal strategies and mucosal barrier protection.